“Aortic aneurysm” is the term used to describe a condition where a segment of the aorta is dilated to a diameter greater than its original diameter. Aneurysms can occur in virtually any region of the vasculature including the aorta in the abdominal and thoracic regions. Aortic aneurysms are caused by hardening of the arteries (atherosclerosis), high blood pressure (hypertension), genetic disposition such as Marfan's Syndrome, trauma, or less common disorders. Atherosclerosis is the most common cause.
Where dilation meets or exceeds 50% of the original aortic diameter, i.e., where the diameter of the aorta is 150% of the original or expected diameter, intervention generally is deemed necessary. Without intervention, the aneurysm may continue to expand, leading to the possibility of tearing or rupture of the aorta, and death. Intervention includes techniques such as replacement of the aorta with a synthetic lumen which is sewn to the two ends of the still viable aorta after the aneurysmal portion has been opened or surgically removed, or, less invasively, by the endovascular placement of an exclusion device such as a stent graft across the aneurysmal site. The stent graft is a tubular member designed to provide a conduit enabling blood flow through the aorta without allowing the systemic pressure of the blood to further stretch the aneurysm. To enable these conditions, the stent graft must extend across the weakened blood vessel wall so that the opposed ends of the stent graft engage and seal against healthy blood vessel tissue to either side of the aneurysm.
A stent graft includes a stent framework (stent portion), which provides physical support of the stent graft in a tubular configuration once deployed at a vascular location, and a graft portion, comprising an excluding material, which is sewn or otherwise attached to the stent portion and which provides a relatively fluid-tight conduit for blood flow through the stent graft and past the aneurysm site. Insertion of a stent graft can be performed without a chest incision using specialized catheters that are introduced through arteries usually at a location in a leg adjacent the groin.
The aorta has numerous arterial branches. For example, the arch of the thoracic aorta has three major branches, all of which arise from the convex upper surface of the arch and ascend through the superior thoracic aperture to the root of the neck. The proximity of an aneurysm to a branch artery may limit the use of an excluding device such as a tubular stent graft, as the main body or ends of the tubular stent graft may occlude or block the branch arteries due to the need to position the stent graft to seal against a healthy, i.e., undiseased or dilated portion of the artery wall. There may be an inadequate length of healthy tissue for the stent graft to seal against in the area between the aneurysmal region of the artery and the location of the branch arteries, or, even if the stent graft initially is located without blocking a branch artery, there still is a risk of migration of the exclusion device to a position where it may partially or fully block a branch artery, since aneurysms of the descending aorta commonly occur above and adjacent to the celiac trunk, superior mesenteric and renal arteries.
Therefore, there is a desire in the art to achieve a greater success of aneurysm repair and healing, and in particular, mechanisms and methods to enable stent grafting or the placement of other exclusion devices adjacent to branch vessels in aneurysmal locations.